Process for the production of methacrylic acid

ABSTRACT

Preparation of aliphatic alpha, beta-unsaturated carboxylic acids from the corresponding saturated acids by oxidative dehydrogenation, at a temperature between 250° and 500° C., in the presence of a catalyst of empirical formula: FeP x  Me y  Me&#39; t  O z  wherein Me is at least one alkali or alkaline earth element, Me&#39; is at least one element selected from the group consisting of Ni, Cu, Ce, Al, Zr, Hf and Pr, x is between 0.2 and 15, y is between 0.01 and 2, t is between 0.01 and 5 and z is such as to satisfy the valencies of the other elements.

BACKGROUND OF THE INVENTION

Aliphatic alpha, beta-unsaturated acids have been already obtained fromthe corresponding saturated acids by a dehydrogenation in the presenceof oxygen on solid catalysts; such catalysts, according to the FrenchPat. No. 2,135,786, are for instance mixed phosphates of iron andbismuth. Still another patent (U.S. Pat. No. 3,948,959) relates to theuse of mixed phosphates of iron and alkali or alkaline earth elements.

DISCLOSURE OF THE INVENTION

In its more general form, the invention concerns a process for theproduction of aliphatic alpha, beta-unsaturated carboxylic acids havingfrom 3 to 8 carbon atoms, by means of an oxidative dehydrogenation at atemperature from 250° to 500° C., of the corresponding saturated acids.The process is characterized in that the catalyst consists of a compoundof the empirical formula:

    FeP.sub.x Me.sub.y Me'.sub.t O.sub.z

wherein Me represents at least one alkali or alkaline earth element, Me'represents at least one element selected from the group consisting ofnickel, copper, cerium, aluminum, praseodinium, hafnium and zirconium, xis between 0.2 and 15, y is between 0.01 and 2, t is between 0.01 and 5and z is such as to satisfy the valencies of the other elements.

There are different possible ways for carrying out the invention; moreparticularly it will be remarked that the process may be realized in acontinuous or discontinuous way. The saturated acid may be fed into thecatalytic reactor in admixture with oxygen or air, or with one or morediluents such as nitrogen, steam, CO₂, etc. The quantity of aliphaticacid in the reacting mixture, in general, is between 1% and 40% byvolume, while the molar ratio oxygen/saturated acid must be, in general,between 0.1/1 and 10/1, but preferably between 0.4/1 and 4/1.

As starting saturated acids may be used with advantageous resultsisobutyric acid and propionic acid for obtaining respectivelymethacrylic and acrylic acid.

The catalytic composition may be used without a carrier and as such itdevelops an excellent catalytic activity. In case one should prefer touse it in combination with a carrier, as such may be used any materialsuitable for the purpose, such as for instance: silica alumina, siliconcarbide, silica-alumina, silicates, borates, carbonates, provided theyare stable under the reaction conditions to which they will besubjected. The quantity of active catalytic compositions, with respectto the weight of the carrier, may vary within a wide range depending onthe characteristics of the carrier itself and on the method used for itspreparation.

The process may be used by employing the catalyst in the form of eithera fixed or a fluidized bed, in this latter case the nature of thecarrier and the method of preparation for obtaining a microspheroidalcatalyst with a suitable granulometric distribution assume a particularimportance. A microspheroidal catalyst may be obtained by varioustechniques. For instance, by spray-drying a solution or suspension ofthe carrier and of the components of the active catalytic composition,or by impregnation of a preformed microspheroidal carrier with asolution of the components of the catalytically active composition.

As starting compounds for the preparation of the catalytic compositionaccording to this invention, for instance may be used the followingcompounds of alkaline metal: nitrates, oxides, hydroxides, carbonates,bicarbonates, nitrites, phosphates, silicates, and the salts ofoxyacids, or mono- or polycarboxylic organic acids such as formates,oxalates, citrates, tartrates, etc.

The iron-, copper-, nickel- and cerium-compounds may be chosen,depending on the method used, from amongst nitrates, chlorides,sulphates, carbonates, salts of organic mono-or polycarboxylic acids,chelates, etc.

Zirconium compounds may be selected from the group comprising nitrate,chloride, sulphate, zirconyl compounds and so on and praseodiniumcompounds may be selected from the group comprising nitrate, oxides,sulphate, chloride, carbonate, salts of organic mono-or poly-carboxylicacids, chelates and so on.

The starting aluminum compounds may be chosen, depending on the methodused, from amongst nitrate, sulphate, salts of organic mono- orpolycarboxylic acids or chelates. For alkali and alkaline earth metalsmay be used: chlorides, sulphates, carbonates, salts of organic mono- orpoly-carboxylic acids, etc., while for the phosphorus may be usedalkaline phosphates, ammonium phosphates, phosphoric and phosphorousacids, etc.

All preparation methods involve a final phase of activation of thecatalytic composition, consisting in a heating of the composition in thepresence of air or of a mixture of air and steam (water vapor), at atemperature between 400° and 700° C. The preparation of the catalyst maybe carried out according to the known methods of the technique of thefield. In the following will be given a few methods by way of examples:

(1) To an aqueous solution of phosphoric acid was added a compound ofelement Me; the mixture thus obtained was thereupon slightly heated (to40°-50° C.) and then was additioned with the iron compound and compoundsof element Me'. The mixture thus obtained was then slowly treated understirring, with 32% ammonia, until reaching a pH value of 6 or 7; it wasthen slowly brought to dryness under constant stirring and the residuewas dried overnight at 130° C. and then activated in the air at 540° C.for 2 hours. The calcined mass was thereupon ground and screened; thefraction between 20 and 35 mesh is suitable for the use in a fixed bedreactor.

(2) A suitable mixture of metal compounds is digested with water andphosphoric acid and then brought slowly to dryness under constantstirring. The residue is then finely ground and then dried at 130° C.,overnight. The mass thus obtained is then activated at 600° C. in theair for 2 hours.

(3) The residue of method 1, dried at 130° C., is treated at 300° C. inthe air. The mass is then ground to below 25 mesh; additioned with 10%of powdery stearic acid, it is then formed into pellets 4×4 mm. Thepellets thus obtained are then activated for 2 hours in the air at 540°C.

(4) A suitable solution of the catalyst components, having a volumecorresponding to that of the carrier, was used for impregnating acommercial microspheroidal silica. The mass thus obtained is allowed torest for 2 or 3 hours, after which it is brought to dryness understirring and then further dried at 130° C. overnight. The product thusobtained is then activated in a fluidized bed in the air for 2 hours at550° C. This same method of preparation is also suitable for preparingcatalysts for fixed beds, by using a suitable carrier.

The use of the catalysts hereinabove allows one to obtain high yields inunsaturated acid and very high conversions of the correspondingsaturated acid without the necessity of carrying out a strong dilutionof the reactants with inert gases such as nitrogen. These results may beascribed to the fact that the catalysts according to this inventionpromote an oxidative dehydrogenation process of regular running andwhich is easily controllable as far as the reaction temperature and thecontact times are concerned.

The reactants may be fed in on the catalyst, already either completelyor partially pre-mixed, or altogether separately. The feeding of thereactants either separately or partially pre-mixed, in general may bemore conveniently applied to a fluid-bed reactor. It is also possible tofeed part of the air or, if desired, also the whole or a part of thesaturated acid into the lower part of the reactor and feed then in oneor more upper points inside the catalytic bed the remaining quantitiesof reactants.

When the reaction is performed within a fixed bed, the catalyst can beplaced inside of the pipes of a tube bundle, while removing the reactionheat by means of suitable fluids circulating on the outside of the tubesand, for instance more commonly, by means of mixtures of molten salts.One may also operate in a reactor consisting of a plurality of adiabaticreaction stages alternated by cooling zones for the cooling of thereacted mixture.

The reaction is carried out at a temperature between 250° C. and 500°C., but preferably between 340° and 440° C. The residence time,expressed in seconds as a ratio between the volume of the catalytic bedand the volumes per second of gaseous mixture of reactants fed in,measured under average temperature and pressure conditions existing inthe catalytic bed, may vary depending on the nature of the catalyticbed, fixed or fluidized, and on the granulometric size of the catalyst.In general it may be between 0.1 and 20 seconds; a preferred time range,corresponding to the most common, practical operational conditions, goesfrom 0.3 to 15 seconds. The total pressure under which the reaction isperformed is not particularly critical and may, thus, vary within a widerange; it is however partly dictated by economical considerations: ingeneral, one operates, thus, at pressures near atmospheric pressure andmore precisely at slightly higher then atmospheric pressure.

The following examples are given with the purpose of furtherillustrating the invention without, however, limiting the same in scope.

EXAMPLE 1

The catalyst was prepared according to the above described Method 1, andmore particularly, there were dissolved 303.3 g of iron nitrate, 50.5 gof potassium nitrate, 145.5 g of nickel nitrate and 222 g of an 85%aqueous phosphoric acid in 600 cm³ of water. This solution was thenslowly treated, under stirring, with 440 cm³ of 32% aqueous ammonia. Theslurry thus obtained was then slowly brought to dryness under constantstirring and then was further dried for 12 hours at 130° C. The productthus obtained was then activated in a muffle for 2 hours at 540° C. Theatomic ratios of the elements in the catalyst were represented by theempirical formula:

    Fe.sub.1.5 Ni.sub.1 K.sub.1 P.sub.3.85 O.sub.z

The oxidative dehydrogenation reaction was carried out in a fixed bedreactor and the fed-in mixture consisted of isobutyric acid, air andwater in the following molar ratios: 1:3:28. The reaction temperatureamounted to 392° C. while the residence time was 0.3 seconds. On thebasis of a gas-chromatographic analysis of the reaction gases, there wascalculated a yield in methacrylic acid of 61.3%, meaning for yield theratio: ##EQU1## Data and results are tabulated in Table I; in said tablethe following definitions of selectivity (s) and conversion (c) areapplicable: ##EQU2## from a short calculation it turns out thatr=c×s×10⁻².

EXAMPLE 2

Example 1 was repeated, but lowering the temperature of the reactiondown to 365° C. and by bringing the residence time to 1 second. Data andresults have been tabulated in Table I.

EXAMPLE 3

Example 1 was repeated, but feeding in isobutyric acid, air and water inmolar ratios of 1:2:28, and by lowering the temperature of reaction to375° C. and bringing the residence time to 1.0 seconds. Data and resultsobtained have been recorded in Table I.

EXAMPLE 4

The catalyst was prepared according to the above described method 1,varying however the atomic ratios of the elements in such a way as toget a product of the empirical formula:

    Fe.sub.1.5 Ni.sub.0.5 K.sub.1 P.sub.3.3 O.sub.z

It was then proceeded as in example 1, bringing the temperature up to390° C. and the residence time to 1.0 seconds. Data and results havebeen recorded in Table I.

EXAMPLE 5

The catalyst has been prepared according to the above described method1, varying the atomic ratios of the elements in such a way as to get acompound of the empirical formula:

    Fe.sub.1.5 Ni.sub.2 K.sub.1 P.sub.4.95 O.sub.z

Thereupon it was proceeded as in example 1, lowering the temperature to360° C. and bringing the residence time to 1.0 seconds. Data and resultsobtained have been recorded in Table I.

EXAMPLE 6

The catalyst was prepared according to example 1, replacing howevernickel by copper so as to obtain a product having the empirical formula:

    Fe.sub.1.5 Cu.sub.1 K.sub.1 P.sub.3.85 O.sub.z

It was then proceeded as in example 1, bringing the temperature to 390°C. and the residence time up to 3.0 seconds. Data and results have beenrecorded in Table I.

EXAMPLE 7

The catalyst was prepared as in example 6, by varying the atomic ratiosof the elements so as to obtain a compound having the empirical formula:

    Fe.sub.1.5 Cu.sub.0.5 K.sub.1 P.sub.3.3 O.sub.z

Thereupon it was proceeded as in example 3, bringing the reactiontemperature up to 410° C. and the residence time down to 0.5 seconds.Data and results have been recorded in Table I.

EXAMPLE 8

The catalyst was prepared according to example 1, replacing nickel bycerium, so as to obtain a compound of empirical formula:

    Fe.sub.1.5 Ce.sub.1 K.sub.1 P.sub.3.85 O.sub.z

The oxidative dehydrogenation reaction was carried out in a reactorloaded with the above catalyst, in the form of a fixed bed.

The fed-in mixture consisted of isobutyric acid, air and water in molarratios of 1:4:28, the reaction temperature was 362° C. while theresidence time was 0.5 seconds. Data and results have been recorded inTable I.

EXAMPLE 9

The catalyst was prepared as in example 8, varying the atomic ratios ofthe elements so as to get a compound of the empirical formula:

    Fe.sub.1.5 Ce.sub.0.5 K.sub.1 P.sub.3.3 O.sub.z

Thereupon the procedure was as in example 1, bringing the temperature ofthe reaction to 375° C. and the residence time to 1.0 seconds. Theresults have been recorded in Table I.

EXAMPLE 10

The catalyst was prepared according to example 8, varying the atomicratios of the elements in such a way as to get a compound of empiricalformula:

    Fe.sub.1.5 Ce.sub.2 K.sub.1 P.sub.4.95 O.sub.z

Thereupon the procedure was as in example 1, bringing the reactiontemperature to 360° C. and the contact time to 0.5 seconds. Data andresults have been recorded in Table I.

EXAMPLE 11

The catalyst was prepared as in example 1, replacing nickel by zirconiumso as to get a compound of empirical formula:

    Fe.sub.1.5 Zr.sub.1 K.sub.1 P.sub.3.85 O.sub.z

The oxidative dehydrogenation reaction was carried out in a reactorloaded with the above catalyst, in the form of a fixed bed. The fed-inmixture consisted of isobutyric acid, air an water in molar ratios1:2.5:28. The reaction temperature amounted to 410° C. and the residencetime was 0.3 seconds. Data and results have been recorded in Table I.

EXAMPLE 12

Example 11 was repeated, except that the fed-in mixture consisted ofisobutyric acid, air and water in a molar ratio of 1:2:28, while thetemperature amounted to 430° C. and the residence time to 0.3 seconds.Data and results have been recorded in Table I.

EXAMPLE 13

The catalyst was prepared as in example 11, replacing zirconium bypraseodinium, so as to obtain a compound of the empirical formula:

    Fe.sub.1.5 Pr.sub.1 K.sub.1 P.sub.3.85 O.sub.z

The procedure was as as in example 11, bringing the reaction temperatureto 390° C. and the residence time to 0.3 seconds. Data and results havebeen recorded in Table I.

EXAMPLE 14

The catalyst was prepared according to example 11, replacing zirconiumby aluminum and varying the atomic ratios of the elements so as to get acompound of the empirical formula:

    Fe.sub.1.5 Al.sub.1 K.sub.1 P.sub.3.65 O.sub.z

Thereupon the procedure was as in example 11, bringing the reactiontemperature to 360° C. and the residence time to 1 second. Data andresults have been recorded in Table I.

EXAMPLE 15

Example 14 was repeated, but the fed-in mixture consisted of isobutyricacid, air and water in molar ratios equal to 1:3:28. The reactiontemperature was brought to 390° C. while the residence time was 1.0second. Data and results have been recorded in Table I.

EXAMPLE 16

The catalyst was prepared according to example 1, replacing potassium bycalcium so as to get a compound of empirical formula:

    Fe.sub.1.5 Ca.sub.1 Ni.sub.1 P.sub.3.85 O.sub.z

Thereupon the procedure was as in example 1, bringing the reactiontemperature to 375° C. and the residence time to 1.0 second. Data andresults have been recorded in Table I.

EXAMPLE 17

Example 16 was repeated, but the fed in mixture consisted of isobutyricacid, air and water in molar ratios of 1:4:28. The reaction temperaturewas 360° C. while the residence time amounted to 0.5 seconds. Data andresults have been recorded in Table I.

EXAMPLE 18

The catalyst was prepared according to example 11, varying the atomicratios of the elements so as to get a compound of the empirical formula:

    Fe.sub.1.5 K.sub.1 Zr.sub.2 P.sub.4.95 O.sub.z

The procedure was as in example 11, but the fed-in mixture consisted ofisobutyric acid, air and water in molar ratios of 1:3:28. The reactiontemperature amounted to 390° C. while the residence time was 0.3seconds. Data and results have been recorded in Table I.

EXAMPLE 19

The catalyst was prepared as in example 12, by varying the molar ratiosof the elements so as to get a compound of empirical formula:

    Fe.sub.1.5 K.sub.1 Zr.sub.0.5 P.sub.3.3 O.sub.z

The procedure was as in example 12, bringing the reaction temperature to390° C. and the residence time to 0.3 seconds. Data and results havebeen recorded in Table I.

                                      TABLE I                                     __________________________________________________________________________                                       Selec-                                                                        tivity                                     Exam-                         Conver-                                                                            metha-                                                                            Other selectivities                    ple Me'.sub.t MeP.sub.x                                                                     (CH.sub.3).sub.2 CHCOOH                                                                T  Time                                                                              sion crylic                                                                            propy-         Yield                                                                             Yield               n°                                                                         (Fe = 1.5; O = z)                                                                       air:H.sub.2 O                                                                          °C.                                                                       (sec.)                                                                            (%)  acid                                                                              lene                                                                              Acetone                                                                            CO.sub.2                                                                         CO (%) time                __________________________________________________________________________    1   NiKP.sub.3.85                                                                           1:3:28   392                                                                              0.3 --   --  --  --   -- -- 61.3                                                                              204                 2   NiKP.sub.3.85                                                                           1:3:28   365                                                                              1   88.4 77.8                                                                              3.0 13.0 5.0                                                                              1.3                                                                              68.8                                                                              68.8                3   NiKP.sub.3.85                                                                           1:2:28   375                                                                              1   79.9 80.7                                                                              3.5 11.1 3.3                                                                              1.4                                                                              64.5                                                                              64.5                4   Ni.sub.0.5 KP.sub.3.3                                                                   1:3:28   390                                                                              1   92.4 74.5                                                                              4.7 14.2 4.4                                                                              2.3                                                                              68.6                                                                              68.8                5   Ni.sub.2 KP.sub.4.95                                                                    1:3:28   360                                                                              1   81.6 74.0                                                                              3.2 16.1 5.8                                                                              0.9                                                                              60.4                                                                              60.4                6   CuKP.sub.3.85                                                                           1:3:28   390                                                                              3   93.0 71.5                                                                              4.4 16.4 4.5                                                                              3.2                                                                              66.5                                                                              22.2                7   Cu.sub.0.5 KP.sub.3.3                                                                   1:2:28   410                                                                              0.5 84.4 75.5                                                                              7.1 12.0 3.0                                                                              2.4                                                                              63.7                                                                              127.4               8   CeKP.sub.3.85                                                                           1:4:28   362                                                                              0.5 78.8 73.4                                                                              2.2 17.4 5.7                                                                              1.3                                                                              57.8                                                                              105.6               9   Ce.sub.0.5 KP.sub.3.3                                                                   1:3:28   375                                                                              1   --   --  --  --   -- -- 73  73                  10  Ce.sub.2 KP.sub.4.95                                                                    1:3:28   360                                                                              0.5 84.4 77.6                                                                              3.2 14.1 3.0                                                                              2.1                                                                              65.5                                                                              131.0               11  ZrKP.sub.3.85                                                                           1:2.5:28 410                                                                              0.3 --   --  --  --   -- -- 76.5                                                                              255.0               12  ZrKP.sub.3.85                                                                           1:2:28   430                                                                              0.3 79.4 79.5                                                                              7.0  9.1 2.7                                                                              1.7                                                                              63.1                                                                              210.3               13  PrKP.sub.3.85                                                                           1:2.5:28 390                                                                              0.3 89.1 78.4                                                                              4.8 12.0 2.5                                                                              2.3                                                                              70  233.3               14  AlKP.sub.3.65                                                                           1:2.5:28 360                                                                              1   85.0 78.8                                                                              2.9 12.6 5.3                                                                              0.5                                                                              67  67                  15  AlKP.sub.3.65                                                                           1:3:28   390                                                                              1   --   --  --  --   -- -- 74.8                                                                              74.8                16  NiCaP.sub.3.85                                                                          1:3:28   375                                                                              1   91.0 76.0                                                                              4.8 11.7 6.2                                                                              1.3                                                                              69.2                                                                              69.2                17  NiCaP.sub.3.85                                                                          1:4:28   360                                                                              0.5 95.8 71.2                                                                              --  --   -- -- 68.2                                                                              136.4               18  Zr.sub.2 KP.sub.4.95                                                                    1:3:28   390                                                                              0.3 94.8 76.2                                                                              3.9 11.7 7.3                                                                              0.9                                                                              72.2                                                                              240.7               19  Zr.sub.0.5 KP.sub.3.3                                                                   1:2:28   390                                                                              0.3 90.8 82.9                                                                              3.0  9.9 3.4                                                                              0.8                                                                              75.3                                                                              251.0               __________________________________________________________________________

EXAMPLE 20

Example 19 was repeated, replacing potassium by cesium so as to get acompound of empirical formula:

    Fe.sub.1.5 Cs.sub.1 Zr.sub.0.5 P.sub.3.3 O.sub.z

Thereupon it was proceeded as in example 19 and were obtained resultsconsiderably better than those of example 19 itself, and even, if onlyslightly, better with respect to the catalysts containing only cesium,that is, lacking zirconium.

We claim:
 1. Process for the production of methacrylic acid by anoxidative dehydrogenation, at between 340° and 440° C., of thecorresponding saturated acid with oxygen in the gaseous phase, theprocess being characterized in that the catalyst consists of a compoundof the empirical formula:

    FeP.sub.x Me.sub.y Me'.sub.t O.sub.z

wherein Me represents at least one alkali or alkaline earth element, Me'represents zirconium, x is between 0.2 and 15, y is between 0.01 and 2,t is between 0.01 and 5 and z is such as to satisfy the valencies of theother elements.